Optical sensor and method of use

An apparatus, comprising:

• a pulsed light source;
• an optical fibre deployed in an environment to be monitored and arranged to receive pulses of light from the pulsed light source;
• an interferometer arranged to receive light backscattered and/or reflected from along the length of the optical fibre as the pulses of light travel along the fibre and to generate an interference signal in dependence thereon, the light being backscattered and/or reflected in dependence on acoustic perturbations incident along the length of the optical fibre, and the interference signal comprising first, second, and third interference signal components having phase shifts therebetween;
• a first photodetector arranged to measure an intensity of the first interference signal component to provide first intensity data;
• a second photodetector arranged to measure an intensity of the second interference signal component to provide second intensity data;
• a third photodetector arrange to measure an intensity of the third interference signal component to provide third intensity data;
• and
• a processor time synchronised with the pulsed light source and arranged to:
• i) receive the first, second and third intensity data and to determine therefrom any optical phase modulation in the received light, and thereby obtain optical phase modulation data from along the length of the optical fibre;
• and
• ii) identify acoustic perturbations incident along the optical fibre in dependence on the determined optical phase modulation, wherein the optical phase modulation data obtained from along, the length of the optical fibre is synchronised to enhance signal sensitivity.